Many materials have been proposed as skin defect wound dressings of burns, donor sites, skin graft site and e.t.c. These dressings are generally classified to those made from synthetic materials and those made from natural materials. Examples of synthetic materials are velour fabric made from nylon fibers or polyester fibers, polyurethane foam sheet, cross-linked polyvinylalcohol foam sheet and the like. Examples of natural materials are collagen nonwoven fabric (commercially available from Meiji-Seika Kaisha Ltd as Meipack), freeze-dried pig-skin (commercially available from Mitsui Pharmaceutical Co. Ltd. as Methaskin) and fibrin membrane. Biological dressings derived from natural materials become more polular as the dressings of skin defect wounds because of high compatibility to a living body.
However, these biological dressings such as collagen nonwoven fabrics or freeze-dried pig-skins have some defects. One of defects is inferior fitnessn to the surface of wounds. Such dressings are required to have an function as an artificial skin to some degree, because it is preferred that the dressings work together with the surface of wounds to heal. In case where the adhesion of the protectors to the surface of wounds is insufficient, much exudates stay between the protector and the surface of wounds and delays drying so as to cause preventing epidermidation. The second defect is that the dressing may be easily decomposed in an early stage. These decompositions not only loss the function of the dressing but also cause infections. As the result the epidermidation is badly affected. The third defect is that it is difficult to absorb the exudate being produced in the surface of the skin. This provides the same result as the first defect. Accordingly, a dressing without having the above defects is desired among the natural materials.
On the other hand, it has been proposed that chitin can be adopted as the wound dressing in the form of nonwoven fabrics composed of chitin fiber, because chitin, which is an aminopolysuccharide containing in exoskeletons of Crustacea, Insecta and the like, has excellent compatibility to a living body when purified. For example, in Proceedings of the 1st Int. Conference on chitin/chitosan (1977), page 300 (hereinafter referred to as "Conference"), chitin nonwoven fabrics are disclosed, wherein the chitin nonwoven fabrics are made by dispersing chitin fibers having a length of 30 mm in water and then removing water. Japanese Patent Publication (unexamined) Nos. 26049/1981 and 16999/1982 also disclose nonwoven fabrics using chitin fibers. Further, U.S. Pat. No. 4,431,601 (corresponding to Japanese Patent Publication (unexamined) No. 77310/1982) discloses chitin fibers having a thickness of 0.5 to 20 denier and a strength of 2 g/d.
These chitin fabrics, however, are not always sufficient as the wound dressings in comparison with the conventional biological dressings. Fiber size is for example 0.15 mm in Conference, 1 to 5 denier in Japanese Patent Publication (unexamined) No. 26049/1981, less than 10 denier (typically 3 denier) in Japanese Patent Publication (unexamined) No. 16999/1982. Japanese Patent Publication (unexamined) No. 16999/1982 does not teach use of binder and Japanese Patent Publication 26049/1981 employs a chitin dope as a binder. Japanese Patent Publication (unexamined) No. 16999/1982 discloses the fiber strength of 1 g/d, but it is not sufficient for wound dressing. Nonwoven fabrics disclosed in the above references have inferior fitness and easy decomposition with exudates, and they are insufficient in the exclusion of the exudate to outside when they are used for the wound dressing.